An R-T-B based sintered magnet has an excellent magnetic properties, thus the R-T-B based sintered magnet is used for various motors such as a voice coil motor (VCM) of a hard disk drive and a motor mounted on a hybrid car, home electric appliances and the like. When the R-T-B based sintered magnet is used for the motors and the like, the sintered magnet is required to have excellent heat resistance and high coercivity to cope with a high-temperature use environment.
As means for improving coercivity (HcJ) of the R-T-B based sintered magnet, in order to improve crystal magnetic anisotropy of a R2T14B phase, a part of a rare earth element R, for which light rare earth elements such as Nd and Pr, are mainly used, is replaced by heavy rare earth elements, such as Dy and Tb. It has tended to be difficult to produce a magnet having coercivity usable for the motors and the like without using heavy rare earth elements.
However, Dy and Tb are scarce resources and expensive as compared to Nd and Pr. In recent years, concern for supply of Dy and Tb has become serious, because demand for high coercivity type R-T-B based sintered magnets which use large amounts of Dy and Tb has rapidly grown. Thus, even with a composition in which use of Dy and Tb is reduced as much as possible, it is required to obtain coercivity necessary for application to the motors and the like.
There have been many proposals for attempting improvement of magnetic properties by changing the composition of the R-T-B based sintered magnet. For example, Patent Literature 1 discloses an R-T-B based sintered magnet for which decrease of coercivity is suppressed in such a manner that an amount of B is reduced to less than a stoichiometric amount so as to suppress generation of a B-rich phase (R1.1Fe4B4) and improve residual magnetic flux density (Br), while Ga is added to suppress generation of a soft magnetic R2Fe17 phase.
Moreover, Patent Literature 2 discloses a rare earth magnet in which variation in magnetic properties is suppressed while Br is improved by reducing an amount of B to less than a stoichiometric amount, and containing elements such as Zr, Ga and Si in combination.